It has been recognized for several years, especially for the purpose of eliminating pollution of water by industrial wastes, that the large quantity of water used in the dyeing of textile materials can be economically replaced by a much more limited quantity of organic solvent or a medium consisting in major part of an organic solvent and in minor part of water. The use of this dye process--termed "solvent dyeing"--, as contrasted with dyeing in a totally aqueous medium, has encountered a number of difficulties, especially for cellulosic fibers and with dyes which have commonly been used therefor.
It has been found in practice that the poor penetration of the fibers (from the surface to the interior) or fabric by the dyestuff produces an irregular or mottled effect, i.e. the fabric is marked with small points of less dense or more dense coloration.
Because of the generally poor solubility of the dyestuff in most of the organic solvents capable of being used in the dyeing process, the dyeing bath is exhausted to only a limited degree and leaves the treating apparatus, at the end of the operation, containing significant quantities of the dyestuff. As a result the process for recovering the solvent to enable its recycling for subsequent dyeing operations and its purification is long, costly and difficult.